Conventionally, a heat exchanger, which includes a core portion in that multiple tubes and outer fins are arranged to be stacked alternately, and a header tank having a through hole through which an end part of each tube are inserted, is known as a heat exchanger for a vehicular air conditioner (e.g., Patent Document 1). In the heat exchanger, the respective components are brazed with each other. In the above-described conventional heat exchanger, the tube is obtained by bending a plate member and fixing both end parts of the plate member to each other, and the tube has a flattened shape in cross section. Accordingly, the tube includes a curved end portion, a pair of flat plate portions opposed to each other, a fixed portion in which one end part of the plate member is bent to hold the other end part of the plate member on an opposite side from the curved end portion, and an inclined portion connecting the fixed portion and the flat plate portion.